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Meningococcal Arthritis — SCE Infectious Diseases MCQ

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HardBone & Joint InfectionMeningococcal ArthritisSCE Infectious Diseases

A 58-year-old man with alcoholic liver disease presents with left knee pain, fever, and a hot swollen joint. Synovial fluid Gram stain shows Gram-negative diplococci that are oxidase-positive. He has not been sexually active for years. What unusual organism should be considered?

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Correct answer: A — Neisseria meningitidis (primary meningococcal arthritis without meningitis)

While Gram-negative diplococci in synovial fluid most commonly suggest N. gonorrhoeae, primary meningococcal arthritis (without meningitis) is a recognised entity, particularly in immunocompromised or complement-deficient patients. N. meningitidis can cause septic arthritis, reactive arthritis, or a combination. The lack of sexual risk factors should prompt consideration of meningococcal species. Both organisms are oxidase-positive Gram-negative diplococci and cannot be distinguished on Gram stain alone — culture and MALDI-TOF are needed.

Reference: BSAC 2020 – Joint infections; UKHSA 2024 – Meningococcal disease